Background information that must be understood before the significance of the present invention can be appreciated includes certain characteristic properties of snow, the nature of known snow shelters, and the usefulness of snow shelters. Understanding of these matters is required to appreciate the obstacles to snow shelter construction in a cold, dry snow environment that the present invention addresses.
A. THE EFFECT OF TEMPERATURE ON SNOW
Many large geographical areas have relatively moderate winter climates where, when snow falls, it is usually wet, slushy or damp. This snow, due to it's relatively warm temperature (near the freezing point) is easily formed into shaped structures, such as snowballs, snowmen and the like. The present invention is not primarily concerned with this type of snow, for with easily molded snow, the present invention does not materially improve on the ability of such snow to be molded into a desired shape.
However, other large geographical areas have colder and drier winter climates where, when snow falls, it is usually dry, cold (well below freezing), powdery and free running. This is the type of snow with which the present invention is primarily concerned. This snow, when pressed together in the manner that one would press together wet, slushy or damp snow as described above, does not easily form into a shaped structure. In fact, this type of snow is often so un-moldable that forming a shaped structure is in practice impossible. In such cold climates, it is only on especially mild days, usually in spring, that the snow is in condition for shaped structures, including snowballs and snowmen, to be made with it.
B. DESCRIPTION AND DEFICIENCIES OF THE TWO COMMON `COLD SNOW ENVIRONMENT` SNOW SHELTERS: IGLOOS AND QUINZHEES
Igloos are dome-shaped snow structures constructed in environments of wind-driven hard packed snow. This snow is cut into blocks and stacked to form a dome shaped shelter. The igloo snow shelter method is limited to tundra or vast open areas where winds blow sufficiently to pack the cold dry snow deeply and over broad areas. The igloo snow shelter method is also limited to those who have the special knowledge necessary to cut and stack the blocks in a very specific pattern.
Quinzhees are constructed by heaping loose snow into a pile, which is hollowed out to provide a chamber. Quinzhees are often used where snow conditions do not permit the cutting of blocks for an igloo. The construction of a quinzhee involves the use of very large volumes of snow because of the material's low angle of repose. That is, a quinzhee pile is a low heap of loose, free running material. It is the kind of shape that one would achieve by pouring sugar, salt or powder in a loose heap. Indeed, some snow textures are referred to as "sugar" or "powder", particularly in downhill skiing environments. The snow pile, once made, must rest for some time for the snow crystals to bond, hardening the pile to the point that it can be hollowed out. This bonding is a characteristic property of snow that is unlike most other free running, powdery materials. The rest period can be short or very long (often up to several hours) depending on snow conditions. A quinzhee once `set-up` after the relatively long waiting period, is hardened throughout the structure so that the snow to be removed to provide a chamber is also hardened, and therefore hard to remove. Quinzhees, due to their irregular shapes, and the necessity of waiting for the snow to harden (a time span not easily determined), are susceptible to collapse.
C. INSULATIVE PROPERTIES OF SNOW
Snow is known to be an excellent thermal insulator. While snow itself is cold, a body of snow will sustain a large thermal gradient. In a test of a shelter constructed according to the present invention, conducted in EMBARRASS, Minn. in February 1997, the external temperature reached -59.degree. Farenheit. Inside the shelter, it was approximately +150.degree. Farenheit, a difference of approximately 74.degree. Farenheit warmer than the outside air. It is to be understood that snow is an abundant and highly insulating building material and that many thousands of people use snow structures as a significant if not critical part of their winter activities.
D. THE CURRENT MARKET
Igloos or snow shelters may be perceived by those unfamiliar with their use as being from the distant past, as being non-progressive or archaic. While it is true that great strides have been made in building technology, it is also a fact that many thousands of people and many institutions such as the Boy Scouts recreationally winter camp, and those in many vocations such as hunters, outfitters, search and rescue personnel, park patrols and the like currently use snow shelters for survival.